Just returned from the Steam and Power show. Still going on thru Monday. Had the greatest time. Must have been at least 8 train Steam engines running and taking passengers around at the same time. Plus cranes and tractors running on steam. Will make sure I go again next year.
Also plenty of food and a flea market.

WGL
Glad that solved you problem.
I have at least one of every style Hudson Rivarossi made. Also have Hudson's made buy Mantua, BLI, and yes IHC made some. IHC made some Canadian versions.
If Bachmann was to make one I would be sure to get some. I have over 40 Bachmann steam engine and they are some of the best made.

Inside the boiler is the front motor bearing that is probably dry. You will have to remove the boiler shell to get at it. Remove the cab handrails. There are 2 screws under the cab and one in the front under the front pilot truck. You might have to remove the pilot truck to get at it. The boiler should lift off. There is also a worm gear inside a cover that could use some grease and 2 bearing on the drive shaft. Not hard to do.
Did you put a drop of oil on each drive wheel axel shaft between the wheel and frame?

ONE WORD   "FANTASTIC"

If you are good with working on small things I have had success with using clear silicon in the groove for traction tires.
On engines with a groove in the wheel I fill it with clear silicone with the engine running upside down in a cradle and smooth it out with a hobby knife. Let dry 24 hours and done.
Bachmann had the tires on backorder at the time.

Didn't cut anything just glued it down in the middle or as far on both ends. Must have gained enough clearance so it would not short out to the frame.

I would fix your 4-8-4 or your track as I have many Bachmann 4-8-4's and none derail on 22in radius. Might be the wheel gauge, something restricting movement of front or rear pilot truck, Draw bar or wires between engine and tender binding. Check the track to see if it is level front to back as well as side to side. Might be a dip in one rail. Does it derail always in the same spot or all over??
You could get an IHC, Rivarossi or Mantua 4-6-4 but you would have to install the DCC. If it is a problem with the track the 4-6-4 might also derail.

I had the same problem on 2 of them. You will see the copper bowed up between the wheel contacts. I used superglue to glue the copper down flat against the plastic bottom plate. Problem solved. You could also put a few coats of paint no the frame and on the copper where it bows up.

Check your local auto parts store. 1/16 pin stripping tape.  Or Ebay.

GG-1's are electric locomotives not diesel. The only sound you would hear is the traction motors making noise as it runs down the track. If you turn on the blower cooling motors you might hear them also. Horn and bell from electric locomotives and that is about it.

I would love to see Bachmann make the K4 in N scale. Also would like several 4-6-2 light and heavy Pacific's. Then throw in a few Hudson's.
They already (under the Graham Farish line) in England make several 4-6-2 steamers. I have a few (nice).
Look at how many would replace there Rivarossi 4-6-2's.

Bachmann are you listening???

Unless you really like to tinker and have very good soldering skill for n scale I would purchase engines with DCC and sound factory installed. Just plugging in a DCC decoder is one thing but making room for a speaker is another. If the system is factory installed the components will match and you have a warranty if something goes wrong. For the price of the separate components you can get them in a new engine already installed.
Shop around.

If this is an 8 wheel drive engine take off the shell, remove the screw on top that holds the truck in and drop the truck down. The screw might be under the electrical board. Locate the female coupling that is slipping on the truck drive shaft slide it toward the motor in the center leaving enough room for the drive shaft and put a drop of superglue on it and the shaft. Then put the truck back in with the drive shaft. Fixed. When you put the screw back on top to hold the truck in don't over tighten as  it will cause the truck to bind and also go in far enough to hit  the worm gear.

When I got my BLI Hudson 1st release some 15+ years ago the motor would run but the engine would not move. Upon inspection the flywheel coupling was spinning loose on the motor shaft. A few drops of superglue fixed it. Been running ever since with no problem pulling a 25+ car train. Never had to re-glue any engines with this problem or fix.

If it's not to late. It is common for the female coupling (universal) on the truck end of the drive shaft to slip or crack. You would have to drop the trucks and replace them or put some superglue on them.
Bachmann should be able to fix as the 8-40c uses the same drive parts. The 8-40c is still available.